1. Field of the Invention
The present invention relates to a golf ball, and more particularly, to the golf ball having an octahedral dimple arrangement which improves the flight performance of the golf ball.
2. Description of the Related Arts
Normally, 300 to 550 dimples are formed on the surface of a golf ball so as to increase the flight distance thereof by improving the aerodynamic characteristic thereof. Of various proposals regarding dimple arrangements, regular octahedral arrangement is most widely adopted because dimples are arranged symmetrically and regularly.
As shown in FIGS. 10, 11 and 12, according to the regular octahedral arrangement, the spherical surface of a golf ball 1 is divided into eight spherical equilateral triangles by projecting, on the spherical surface of the golf ball 1, the ridge lines 2a of a regular octahedron 2 inscribing the spherical surface of the golf ball 1 and dimples are equivalently arranged in each spherical triangle as shown in FIG. 12. The ridge lines 2a projected on the spherical surface of the golf ball 1 form three great circles 3, 4, and 5 on which dimples 6 are not arranged. That is, the golf balls 1 has on the surface thereof three great circles which do not intersect the dimples 6.
Normally, since the golf ball is molded by a pair of upper and lower semispherical molds, dimples are not arranged on the seam between the upper and lower molds so as to facilitate the removal of a burr formed when the golf ball is molded. Therefore, in the regular octahedral dimple arrangement, the great circle 3 coincides with the seam.
The main object of the dimple is to accelerate the transition of the turbulent flow of a boundary layer and increase the aerodynamic characteristic of the golf ball in order to increase the flight distance of the golf ball. Therefore, it is well known to those skilled in the art to effectively arrange dimples to accelerate the transition of the turbulent flow of the boundary layer. From this point of view, various proposals have hitherto been made to improve the regular octahedral dimple arrangement on the surface of the golf ball. According to the dimple arrangement proposed by Japanese Patent Laid-Open Publication No. 62-79072 (unexamined), dimples of large and small diameters are arranged on the surface of the golf ball. According to the dimple arrangement proposed by Japanese Patent Laid-Open Publication No. 2-152476 (unexamined), dimples of more than three different diameters are arranged on the surface of the golf ball.
The regular octahedral dimple arrangements proposed by these prior patent applications are capable of improving the flight performance of the golf ball to some extent, however, there is still a problem due to three great circles being formed on the golf ball.
Namely, when the golf ball flies with backspin, dimples arranged on a circumference which rotates fastest in its backspin have the most affect on the flight distance of the golf ball. When the circumference which rotates fastest in its backspin coincides or approximately coincides with a great circle having no dimples arranged thereon, dimple effect is reduced, so that the flight distance of the golf ball becomes shorter. In the octahedral dimple arrangement, there is a great possibility that the circumference which rotates fastest in its backspin coincides or approximately coincides with one of the three great circles because the golf ball has three great circles unintersecting dimples. Therefore, the flight distance of the golf ball is varied due to one of the great circles formed thereon.